Cholera in Vietnam: Changes in genotypes and emergence of class I integrons containing aminoglycoside resistance gene cassettes in Vibrio cholerae O1strains isolated from 1979 to 1996

The number of cholera cases and the mortality rates reported from different regions of Vietnam varied considerably in the period from 1979 to 1996, wi th between 2,500 and 6,000 cases reported annually from 1992 to 1995, Annua l mortality rates ranged from 2.0 to 9.6% from 1979 to 1983 to less than 1. 8% after 1983, Major cholera outbreaks were reported from the High Plateau region for the first time in 1993 and 1995; this is an area,vith limited ac cess to health services and safe drinking-water supplies, All cases were as sociated with Vibrio cholerae O1, Using ribotyping, cholera toxin (CT) geno typing and characterization of antibiotic susceptibility patterns and antib iotic resistance genes by PCR, He show that strains isolated after 1990 wer e clearly different from strains isolated before 1991, In contrast to strai ns isolated before 1991, 94% of 104 strains isolated after 1990 showed an i dentical ribotype R1, were resistant to sulfamethoxazole and streptomycin, and showed a different CT genotype, Furthermore, PCR analysis revealed that sulfamethoxazole-resistant strains harbored class I integrons containing a gene cassette ant(3 ")-1a encoding resistance to streptomycin and spectino mycin. This is, to our knowledge, the first report of class I integrons in I cholerae. The development of cholera and the changes in the phenotypic an d genotypic properties of I: cholerae O1 shown in the present study highlig ht the importance of monitoring V. cholerae O1 in Vietnam as in other parts of the world, In particular, the emergence of the new ribotype R1 strain c ontaining class I integrons should be further studied.